This project will study the hypothesis that human neural stem cells (hNSCs) implanted into monkeys can normalize parkinsonism resulting from the neurotoxin 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP). These primordial, uncommitted, pluripotent cells can be propagated in large numbers and then safely differentiated into most cell types of the nervous system, including dopamine-producing neurons. NSCs migrate to populate developing or degenerating brain regions, perhaps allowing a more functionally correct and effective reconstruction. Pilot studies now show engraftment of hNSCs in the brain of fetal, neonatal, infant, and adult monkeys, for at least a month. Dopamine depleted adult monkeys showed graft-derived tyrosine hydroxylase positive cells and appropriate migration from the site of injection to dopamine-depleted areas. This project will test hypotheses in monkeys: (1) that hNSCs will survive, differentiate, and integrate in the brain of normal adult monkeys without immunological rejection or harmful overgrowth; (2) that hNSCs will eliminate parkinsonism after MPTP treatment, and that the presence of dopamine injury will influence their distribution and fate. NSCs will be identified and quantitated using genetic markers, immunohistochemistry, and multi-synaptic tract tracing. The following will be characterized and compared in normal monkeys and monkeys after MPTP: hNSC survival, migration, cell division, differentiation, connectivity, immunogenicity, stability of expression of a transgene (LacZ), apoptosis, and effect of host environment on all of these. In the dopamine-depleted parkinsonian monkey, dopamine and its metabolite concentrations, autoradiography of dopamine transporters, behavioral reversal of parkinsonism, dose effects, and synaptic connections will be studied over time courses of 7 days, 1, 3, 6, and 12 months. Comparisons will also be made with effects of primary fetal ventral mesencephalic tissue transplants in parkinsonian monkeys from prior and parallel studies. These studies will advance our understanding of the neurobiology and safety of human neural stem cells in a well established clinically relevant primate model of Parkinson's disease, and, if successful, support safe clinical studies in patients with Parkinson's disease in the future. The results will also advance understanding of useful methods for studying and treating a broad range of neurodegenerative, genetic, and traumatic conditions of the nervous system.